Method for electrolyte injection

ABSTRACT

An electrolyte injection method for injecting an electrolyte into a battery case tightly closed except an electrolyte injection hole, said method comprising an electrolyte injection nozzle airtightly mounted on the electrolyte injection hole, exhausting the space inside the battery case with the electrolyte injection nozzle mounted on the electrolyte injection hole, an electrolyte pot connected to the electrolyte injection nozzle via an electrolyte injection valve and for storing the electrolyte to be injected into the battery case, and feeding a given amount of the electrolyte into the electrolyte pot via an electrolyte feeding valve, and injecting the electrolyte in the electrolyte pot under pressure into the battery case, whereby the pressurized gas feeding means is connected to the electrolyte pot via a pressure valve, and the electrolyte is injected by pressurizing the electrolyte after exhausting internal space of the battery case.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and a method forelectrolyte injection. The invention relates to an apparatus and amethod for efficiently injecting electrolyte through a small hole on abattery case or a top cover after the cover is mounted on the batterycase where a battery element is accommodated, and in particular, to anapparatus and a method for injecting electrolyte suitable for injectionof electrolyte to a nonaqueous electrolyte battery such as lithium ionbattery.

As power source for small size electronic devices, various types ofbatteries are used. As the power source for the devices such as handyphone, notebook-sized personal computer, cam-corder, etc. nonaqueouselectrolyte secondary battery such as lithium ion secondary battery,i.e. small-size large-capacity sealed battery, is used. As thenonaqueous electrolyte battery, cylindrical type and rectangular typebatteries are generally used.

The lithium ion battery, used as a power source for small sizeelectronic devices, is produced as follows: Active materials are coatedon each of a positive electrode current collector and a negativeelectrode current collector. The positive electrode and the negativeelectrode thus produced are laminated with a separator interposedbetween them, and this is wound up to form a battery element, which isthen accommodated in a battery case and sealed.

FIG. 4 shows the drawings to explain assembling process of the battery.

As shown in FIG. 4 (A), the battery element is accommodated in a batterycase 41. On an open upper portion of the battery case 41, there areprovided an external electrode leading terminal 44, an electrolyteinjection hole 43, and a top cover 45 with a pressure release valve toprevent rupture of the battery when the pressure inside the battery isincreased, and these are mounted on the battery case by means such aslaser welding. As shown in FIG. 4 (B), an injection nozzle 47 of anelectrolyte injection apparatus 46 is airtightly retained on theelectrolyte injection hole 43 on the top cover 45. Exhaust means 49 ofthe electrolyte injection apparatus 46 is driven and an exhaust valve 50is opened. Then, the air in the battery case is drawn out to attain apredetermined degree of reduced pressure. A predetermined amount ofelectrolyte 53 is then injected to an electrolyte pot 51 via anelectrolyte feeding valve 56 by electrolyte feeding means 55. Afterinjecting the predetermined amount of electrolyte, the electrolytefeeding valve 56 is closed.

Next, as shown in FIG. 4 (C), the exhaust valve 50 is closed, and theelectrolyte injection valve 52 is opened. Then, the electrolyte in theelectrolyte pot 51 is injected into the battery case due to the pressuredifference between air pressure in the battery case and the atmosphericpressure applied on a vent hole 57 of the electrolyte pot. After theelectrolyte is injected into the battery case, a metal piece is mountedon the electrolyte injection hole, and the injection hole is welded forsealing.

In case of a lithium ion secondary battery, the battery elementaccommodated in the battery case is produced as follows: A negativeelectrode material such as carbonaceous material, on which lithium canbe doped or undoped, is coated on a band-like current collector and anegative electrode is prepared. A positive electrode material such aslithium transition metal composite oxide, e.g. lithium cobaltate,lithium manganate, etc. is coated on a band-like current collector, anda positive electrode is prepared. These negative and positive electrodesare laminated with a separator interposed between them, and this iswound up to form a battery element.

In the battery case with the battery element accommodated in it, a largenumber of small voids are formed. Even when the air in the internalspace of the battery case has been drawn out, long time is required forcompletely exhausting the voids. Further, some time is required untilthe nonaqueous electrolyte is permeated into the battery element, and itis very difficult to inject the electrolyte within short time.

In the method as described above, the driving force for the injection ofthe electrolyte into the battery case is the pressure difference causedby the reduced pressure, and it does not reach the level of more thanone atmospheric pressure.

JP-07099050(A) describes an apparatus, comprising a battery arranged ina chamber and with an electrolyte to be injected into it, and apredetermined amount of electrolyte is filled in an electrolytereservoir mounted on the injection nozzle. Then, the pressure in thechamber is reduced, and gas such as the air in the electrolyte or thebattery element is removed. Then, the pressure is restored to theatmospheric pressure, and pressure is applied again, and the electrolyteis injected.

In this apparatus, however, a funnel-like member with a reservoircorresponding to the amount of the electrolyte to be injected is mountedwhile the top portion of the battery base with the battery element isopened, and the space inside the battery case is exhausted. A part ofthe electrolyte is injected into the battery case before exhausting andis permeated into the battery element. As a result, the exhausting fromthe voids in the battery element is insufficient because of the presenceof the electrolyte. Exhausting is performed while the electrolyte ispresent in the reservoir, which comprises a funnel-like member on thetop portion of the battery case, and the pressure is applied as theatmospheric pressure. As a result, air bubbles are generated when theair passes through the funnel-like unit from inside the battery case,and these air bubbles are sent into the battery.

Also, this apparatus is applied to the battery assembling process toinject the electrolyte before the top cover is mounted on the topportion of the battery case. This cannot be applied to the method, inwhich the electrolyte with higher viscosity is injected through smallelectrolyte injection hole of less than 1 mm in diameter of a smallrectangular type battery as arranged on the top cover on the open upperportion of the battery case.

It is an object of the present invention to provide an electrolyteinjection apparatus, by which it is possible to quickly fill theelectrolyte to all corners inside the battery case. It is another objectof the present invention to provide an apparatus and a method forinjecting the electrolyte, by which the electrolyte can be easilyinjected even in case of a small size rectangular battery.

SUMMARY OF THE INVENTION

The present invention provides an electrolyte injection apparatus forinjecting an electrolyte into a battery case tightly closed except anelectrolyte injection hole, said apparatus comprising an electrolyteinjection nozzle airtightly mounted on the electrolyte injection hole,exhaust means for exhausting the space inside the battery case with theelectrolyte injection nozzle mounted on the electrolyte injection hole,an electrolyte pot connected to the electrolyte injection nozzle via anelectrolyte injection valve and for storing the electrolyte to beinjected into the battery case, and electrolyte feeding means forfeeding a given amount of the electrolyte into the electrolyte pot viaan electrolyte feeding valve, and pressurized gas feeding means forinjecting the electrolyte in the electrolyte pot under pressure into thebattery case.

Also, the present invention provides the electrolyte injection apparatusas described above, wherein there is provided pressurizing means forpreventing deformation of the battery case by applying pressure on wallsurfaces of the battery case when the pressurized gas is fed to theelectrolyte pot via the pressure valve from the pressurized gas feedingmeans.

Further, the present invention provides an electrolyte injection methodfor injecting electrolyte into a battery case tightly closed except anelectrolyte injection hole, said method comprising the steps ofexhausting internal space of the battery case to a predetermined degreeof reduced pressure, storing a predetermined amount of electrolyte in anelectrolyte pot, feeding a pressurized gas into the electrolyte pot atthe same time or after the starting of the injection of the electrolyteof the electrolyte pot into the battery case, and injecting theelectrolyte under pressure into the battery case.

Also, the present invention provides the electrolyte injection method asdescribed above, wherein deformation of the battery case is prevented byapplying pressure on wall surfaces of the battery case when theelectrolyte is fed under pressure by the pressurized gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing to explain an electrolyte injection apparatusaccording to the present invention;

FIGS. 2A-2C represents drawings to explain operation of an electrolyteinjection apparatus of the present invention;

FIG. 3 is a perspective view to explain means for preventing deformationof the battery case; and

FIGS. 4A-4C shows drawings to explain assembling process of a battery.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

According to the present invention, after the air remaining in a batterycase has been removed by air exhausting, an electrolyte is suppliedunder pressure into a battery case. As a result, the electrolyte can bequickly injected through a small injection hole for the electrolyte.

Detailed description will be given below on the present inventionreferring to the drawings.

FIG. 1 is a drawing to explain an electrolyte injection apparatus of thepresent invention.

A battery element 2 is accommodated in a battery case 1. On an openupper portion of the battery case 1, there are provided an electrolyteinjection hole 3, an external electrode leading terminal 4, and a topcover 5 with a pressure release valve to prevent rupture of the batterywhen pressure inside the battery is increased, and these are attached onthe battery case 1 by means such as laser welding. An injection nozzle 7of an electrolyte injection apparatus 6 is mounted on the electrolyteinjection hole 3. The injection nozzle 7 is provided with airtightnessmaintaining means such as O-ring 8 so that airtightness is maintainedwhen it is pressed against wall surfaces of the top cover.

The electrolyte injection apparatus comprises exhaust means 9 forexhausting the space in the battery case, and an exhaust valve 10, whichconnects the injection nozzle 7 with the exhaust means 9.

An electrolyte pot 11 for accommodating a predetermined amount ofelectrolyte is connected to the injection nozzle 7 via an electrolyteinjection valve 12. Electrolyte feeding means 15 connected with storagemeans 14 of an electrolyte 13 is coupled to the electrolyte pot 11 viaan electrolyte feeding valve 16.

Pressurized gas feeding means 17 is connected to the electrolyte pot 11via a pressure valve 18.

FIG. 2 shows drawings to sequentially explain operation of theelectrolyte injection apparatus of the present invention.

As shown in FIG. 2(A), the battery element is accommodated in thebattery case, and a top cover 5 with the electrolyte injection hole 3 ismounted on the open upper portion of the battery case 1 by means such aslaser welding. The injection nozzle 7 of the electrolyte injectionapparatus 6 is airtightly attached to the electrolyte injection hole 3.Next, the exhaust means 9 is operated, and the exhaust valve 10connecting the injection nozzle 7 with the exhaust means 9 is opened,and the air in the battery case is drawn out. From the electrolytefeeding means 15, a given amount of electrolyte corresponding to thebattery volume is injected to the electrolyte pot 11.

Next, as shown in FIG. 2(B), the exhaust valve 10 and the electrolytefeeding valve 16 are closed, and the electrolyte injection valve 12 isopened. Because the pressure inside the battery case is reduced, theinjection of the electrolyte into the battery case is started due to thedifference of the pressure between the space inside the battery case andthe electrolyte pot 11.

When the injection of the electrolyte of the electrolyte pot 11 isstarted, as shown in FIG. 2(C), the pressure valve connected to thepressurized gas feeding means 17 is opened. Pressure is applied on theelectrolyte in the electrolyte pot 11, and the electrolyte can bequickly injected into the battery case.

In the electrolyte injection apparatus of the present invention,pressure is applied inside the battery case when the electrolyte isinjected into the battery case. Depending on size, type, etc. of thebattery case, wall surfaces of the battery case may be swollen ordeformed. In this respect, it is preferable that the deformation of thebattery case caused by swelling is suppressed when the pressure isapplied inside the battery case.

In the above, description has been given on the method to inject theelectrolyte of the electrolyte pot under pressure after injecting agiven amount of electrolyte into the electrolyte pot. If pressurizedfeeding means for feeding a given amount of electrolyte under pressureis used, it is possible to directly inject the electrolyte underpressure without using the electrolyte pot.

FIG. 3 is a perspective view to explain means for preventing deformationof the battery case.

After the injection of the electrolyte through the electrolyte injectionnozzle 7 has been started, the pressure valve 18 is opened, and pressureis applied on the electrolyte in the electrolyte pot 11. Then, wallsurfaces 21 of the battery case are pressurized from both sides bypressurizing means 20, and deformation of the wall surfaces 21 of thebattery case 1 is prevented.

The pressure applied on the wall surfaces of the battery case is apressure corresponding to the pressure of the electrolyte to be injectedinto the battery case, and it is preferable to apply pressure equal tothe pressurizing force.

Operating conditions of the electrolyte injection apparatus of thepresent invention can be set as desired according to type of batteryactive material, shape and structure of the battery, etc. When the airin the battery case is drawn out and the pressure is reduced to lowerthan 8-10 Torr within 5-7 seconds, the condition is maintained for about2 seconds. After confirming that the degree of vacuum is stable andthere is no leakage, the exhaust valve is closed, and the injection ofthe electrolyte is started. After 4-10 seconds from the initiation ofthe injection of the electrolyte, the pressure valve is opened to applypressure.

As the gas to be used for pressurizing the electrolyte, any type of gasmay be used so far as it does not react with or deteriorate theelectrolyte. It is preferable to pressurize using nitrogen or carbondioxide, which is completely free of moisture. Pressuring force may be0.8-2 kgf/cm².

According to the method of the present invention, electrolyte can beinjected in 60 seconds through the electrolyte injection hole of 1 mm indiameter into a battery of 48×30×6 mm (height×length×width).

In the electrolyte injection apparatus of the present invention, theelectrolyte is stored in the electrolyte pot while the space inside thebattery case is being exhausted, and the electrolyte is pressurized bythe pressurizing means and is injected into the battery case. As aresult, even through a small electrolyte injection hole on the batterycase, the electrolyte can be injected within short time.

What is claimed is:
 1. An electrolyte injection method for injectingelectrolyte into a battery case tightly closed except an electrolyteinjection hole, said method comprising the steps of exhausting internalspace of the battery case to a predetermined degree of reduced pressure,storing a predetermined amount of electrolyte in an electrolyte pot,feeding a pressurized gas into the electrolyte pot at the same time orafter the starting of the injection of the electrolyte of theelectrolyte pot into the battery case, and injecting the electrolyteunder pressure into the battery case.
 2. An electrolyte injection methodaccording to claim 1, wherein deformation of the battery case isprevented by applying pressure on wall surfaces of the battery case whenthe electrolyte is fed under pressure by the pressurized gas.